Speaker
Description
We studied the feasibility of implementing cryogenic bolometry for rare-event searches with the temperature-sensitive, high-Q whispering gallery mode in a sample of single-crystal calcium tungstate (CaWO$_4$) and present conservative estimates of the minimum energy threshold on the order of MeV.
Solid-state detectors for rare-event searches typically utilise a crystalline target coupled to high-sensitivity thermal transducers. Light dark matter (LDM) is hypothesised to undergo elastic scattering with target nuclei or electrons, necessitating detectors capable of resolving $\mu$K temperature fluctuations. Dual-channel detection is standard practice for signal discrimination, pairing bolometry with either scintillation or ionisation (charge) channels to differentiate between electron and nuclear recoils. This investigation focused on advancing the thermometry limit of established cryogenic bolometers. Transition Edge Sensor (TES) bolometers, amongst other LDM detectors, are currently limited by low-energy excess (LEE) noise. While the origin of LEE remains speculative, it is frequently attributed to dark currents, shot noise, lattice strain, and Kapitza resistance at the sensor-target interface. It is hypothesized that these noise sources are exacerbated by the external nature of the sensors and attempts to alleviate mounting strain have been pursued.
We propose utilising the target crystal itself as the transducer; coupling high-Q WGM resonances with zero-field spin transitions to circumvent interface-related noise and strain-induced artifacts. Spin-photon coupling induces frequency detuning (∆f). This non-linear interaction provides a temperature coefficient (α) of the dielectric permittivity ($ϵ_{r}$). The mechanism is driven by dilute spin ensembles originating from paramagnetic impurities or intrinsic colour centers within the CaWO$_{4}$ matrix at zero magnetic field (ZF). The method presented establishes a promising way forward for conducting cryogenic bolometry that will complement mature TES-based cryogenic bolometers, potentially ruling out LEE noise.
| Primary Abstract Topic | Experiment: WIMPs |
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